Process for the production of esters and carboxylates of alkyl boric acids



i United States Patent 3,133,951 PROCESS FOR THE PRODUCTION OF ESTERS AND CAREOXYLATES ()F ALKYL BORIC ACIDS Karl Niitzel and Konrad Lang, Leverkusen, Germany, assignors to Farbenfahriken Bayer Aktiengesellschaft, Leverkusen, Germany, a corporation of Germany No Drawing. Filed Nov. 3, 1960, Ser. No. 66,933 Claims priority, application Germany Nov. 5, 1959 8 Claims. (Cl. 260-462) Various processes for the production of esters and carboxylates of alkyl boric acids have already become known. They have, however, substantial defects and can be carried out on a technical scale only with difiiculties.

Thus, the preparation of alkyl boric acid esters by conversion of boric acid esters with alkyl metal compounds is known. These alkyl metal compounds such as Grignard compounds and aluminium alkyls, are highly sensitive to air and moisture and are, therefore, not suitable for technical processes. They require great expenditure of apparatus and on account of their violent reaction with water may lead to explosions. The same disadvantages are characteristic of processes for the esterification of free alkyl boric acids since these alkyl boric acids are mostly produced by means of metal-organo compounds.

A partial oxidation of boron trialkyls which is rather difficult to obtain technically also does not lead to uniform reaction products. The reaction of boron trialkyls with boric acid esters proceeds only at 200 C. at an appreciable rate. At this temperature, however, isomerisation reactions occur so that sensitive alkyl boranes and boric acid esters cannot be subjected to this reaction. The addition of boron halides does not improve the reaction conditions.

Mixed anhydrides of alkyl boric acids with carboxylic acids could hitherto be prepared only by the reaction of carboxylic acids with the boron trialkyls which are difiicult to obtain, and with the splitting ofi of alkane.

The object of the present invention is to provide a process for the production of esters and carboxylates of alkyl boric acids which consists in reacting alkyl diboranes with organic hydroxyl group-containing compounds of the formula ROH, wherein R' stands for alkyl-, aminoalkyl-, alkylaminoalkyl-, alkoxyalkyl, dialkylaminoalkyl, aromatic and acyl-radicals.

Hydroxyl group-containing organic compounds according to the invention include alcohols, phenols and carboxylic acids.

The esters and carboxylates of alkyl boric acids obtainable according to the invention are illustrated by the following two formulae in which the alkyl borane derivatives contain either one or two alkyl groups:

In the above formulae R denotes an aliphatic or cycloaliphatic hydrocarbon radical as for example, methyl-, ethyl-, propyl-, butyl-, amyl-, hexyl-, octyl-, nonyl-, decyl-, dodecyl-, hexadecyl-, octadecyl-, cyclopentylor cyclohexylradical, and R denotes an aliphatic, aromatic or acyl radical as for example alkylradicals such as methyl, ethyl, propyl, butyl, amyl, hexyl, octyl, nonyl, decyl, dodecyl, hexadecyl, cyclopentyl, cyclohexyl; aminoalkylradicals as, for instance aminoethyl, aminopro-pyl, aminobutyl, aminoamyl, aminodecyl, aminododecyl, aminooctadecyl preferably the 06- and (S-substituted radicals; alkylaminoalkyl radicals as, for instance the methylamino-, dimethylamino-, ethylamino-, diethylamino-, propylamidipropylarnino-, hexylaminoand decylamino-substituted derivatives preferably the ocand [it-substituted derivatives of the aforementioned alkylradicals; alkoxy- (C H -phenyl), C1QHI7CO- (c oHq-naphthyl) and the amino-, methylamino-, dirnethylamino-, propylamino-, dipropylarnino-, methoxyethoxy-, propoxy-, butoxyand halosubstituted derivatives of these acylradicals, preferably the a, B- and ortho-substituted derivatives. Depending on the meaning of R, the compounds according to the invention are alkyl boric acid alkyl esters, alkyl boric acid aryl esters or mixed anhydrides of alkyl boric acids and carboxylic acids respectively.

The invention is characterized in that an alkyldiborane of the formula R,,B H is contacted with an organic hydroxyl group containing compound of the formula R'OH, wherein R and R have the aforementioned meaning, until one mol hydrogen per mol organic hydroxyl group containing compound employed is evolved and then the boron compound RB(OR') or R BOR' formed is recovered. The alkyl diboranes used as starting materials are dimers of alkyl boranes. The composition of the dimers corresponds to the general formula R B H wherein R denotes an alkyl or cycloalkyl radical for example methyl, ethyl, propyl, butyl, amyl, hexyl, octyl, nonyl, decyl, dodecyl, octadecyl, hexadecyl, cyclopentyl, cyclohexyl and ham integer from 1 to 4. In order to simplify the reaction schemes, the formula of the dimeric alkyl diboranes is not indicated in the following, but in each case the formula of the corresponding monomeric form. The general formula of the monomeric alkyl boranes corresponds to the general formula of the dimeric boranes wherein R denotes an alkyl radical and m the number 1 or 2.

The process according to the invention may be represented by the following reaction equations:

Alkyl boric acid alkyl ester C H BH +2C H OH C H B (OC H +2H Dialkyl boric acid aryl ester a 'r) z s 5 3 1) 2 e s 2 Dialkyl boric acid-methylcarboxylate The reaction of alkyl diboranes with the hydroxyl group-containing organic compounds can be carried out without difliculty. A great advantage is the fact that the operation can be carried out at low temperatures. In order to avoid any side-reactions which may occur by the splitting off of hydrocarbon radicals from the alkyl diborane, the reaction is advantageously carried out at tem peratures within the range of -25 to +50 C., preferably between 10 to +50 C. Only the reaction of alkyl diboranes with aminocarboxylic acids requires the application of higher temperatures, approximately between 20 and 150 C.

The use of solvents can be an advantage in some cases, but is not necessary in principle. Especially advantageous is occasionally the use of solvents which promote the dissociation of the alkyl diboranes into monomeric alkyl borane preceding the reaction. These solvents include aliphatic and cycloaliphatic ethers such as diethylether, dipropylether, di-isopropylether, dimethylethers of mono-, di-, triand tetraethyleneglycol and tetrahydrofuran. In solvents of this type, the reaction between alkyl diborane and organic hydroxyl compounds starts already at a lower temperature than in a solvent-free system or when using solvents which do not accelerate the dissociation to such an extent as, for example, hydrocarbons.

On account of the reactivity of the alkyl diboranes towards air and water, the operation is carried out in an inert gas atmosphere and with the exclusion of moisture. Starting materials and end products of the process according to the invention are, however, by far not so reactive as e.g. aluminium alkyls. For this reason, the carrying out of the reactions on a technical scale, is essentially simpler.

The reaction is carried out by mixing the two reactants alkyl diborane and organic hydroxyl group containing compound in portions, care being taken for the removal of the reaction heat. The reaction is completed by subsequent slight heating. Since practically no side-reactions occur when suitably choosing the reaction temperature, the purity of the reaction product obtained is in accordance with the starting materials so that in many cases a special purification of the reaction products can be dispensed with.

Special embodiments of the invention are the reaction of alkyl diboranes with alkoxy alcohols, aminoalcohols, and aminocarboxylic acids. If these reactants are chosen in such a manner that by the coordinative linkage of the basic centre (functional group with single electron pairs such as amino-nitrogen, ether-oxygen) to the boron atom, a ring molecule, preferably a 5- or 6-membered ring, can be formed or a coordinative saturation occurs by a pairformation or the formation of chain-shaped aggregates, compounds are obtained which, in contrast to the airand water-sensitive alkyl boric acid esters or alkyl boric acid carboxylates, show a surprising stability to oxidation and hydrolysis.

Thus, for example, by the reaction of tetrapropyldiborane with fi-methoxybutanol there is obtained the following ring molecule:

The group of these ring-shaped B,B-dialkyl-O-alkylboro-2,6-dioxanes represents a new class of very stable compounds previously not described in the literature.

In analogous manner the reaction of a-alkoxy alcohols leads to S-membered rings.

The reaction of tetraalkyl-diborane with aor Si-aminoalcohols leads to the corresponding 5- or 6-membered rings, the boro-oxazolidines or tetrahydro-boro-oxazines which show substantial stability to air and water and which were hitherto obtainable only by the reaction of alkylboric acids with aninoalcohols. Correspondingly, compounds having double rings can be obtained by the reaction of dialkyl-diboranes with diethanol-amines.

The reaction of tetraalkyl-diboranes with u-amino- B NH,

(C H7)2BH HO.CO.CHZ.NH O l B-dipropyl-borooxazolidone For the formation of ring-shaped compounds it is advantageous to operate in solvents or suspensions.

The compounds obtained according to the process of the invention still contain alkyl groups bound to boron atoms. These can further be reacted, especially at temperatures above 100 C., in analogous manner to the trialkyl boranes, with phenols, alcohols, mercaptans and other compounds containing acid hydrogen atoms.

By the process according to the invention the esters and carboxylates of alkyl boric acids are readily obtainable. This is not only due to the simple process, but also to the fact that the starting materials are easily obtainable. The compounds according to the invention are valuable intermediates for the synthesis of pest control agents, and themselves can be used directly as additives for fuels in an analogous manner to the boron compounds mentioned in the German Patents No. 1,079,384 and 1,066,383 and as lubricants.

Alkyl-diboranes can be produced, for example, by the reaction of sodium borohydride with corresponding olefines in the presence of boron trifluoride. Instead of olefines, trialkyl boranes may also be used.

The following examples are given for the purpose of illustrating the invention.

Example 1 74 g. (1 mol) of n-butanol are placed in a three-neck flask provided with stirrer, reflux condenser and dropping funnel under nitrogen. 98 g. (0.5 mol) of tetrapropyldiborane are slowly added dropwise with strong external cooling with ice. Hydrogen escapes. The mixture is subsequently heated to 35 C. for /2 hour. The dipropyl boric acid butyl ester formed in more than 90% yield boils at 40 C./0.95 mm. Hg39 C./0.72 mm. Hg.

Example 2 60 g. (1 mol) of n-propanol are reacted with 98 g. of tetrapropyl diborane at 10 C. as described in Example 1. The dipropyl boric acid propyl ester formed in the same high yield boils at 5055 C./ 6 mm. Hg.

Example 3 94 g. (1 mol) of phenol are reacted at -l0 C. with 98 g. of tetrapropyl diborane as described in Example 1. The dipropyl boric acid phenyl ester formed in about yield boils at 67 C./3 mm. Hg.

Example 4 50 g. of tetrapropyl diborane are placed in a three-neck flask provided with dropping funnel, reflux condenser and stirrer. 45 g. of B-methoxy-butanol are added dropwise with stirring in the course of 60 minutes. With the evolution of hydrogen the temperature rises to 45 C.; it is maintained by air-cooling.

Distillation of the product shows that after slight first runnings a nearly yield (referred to tetrapropyl diborane) of dipropyl boric acid-S-methoxybutyl ester is Example 50 g. of tetrapropyl diborane are introduced into a three-neck flask provided with dropping funnel, reflux condenser and stirrer. 45 g. of methoxyacetic acid are added dropwise with stirring and strong cooling within 60 minutes. During the exothermic reaction hydrogen escapes. The yield of dipropyl methoXyaceto-boric acid is 86% of the theoretical, B.P. 95 C./2 mm. Hg.

Example 6 75 g. (1 mol) of glycine are suspended in 200 ml. of o-xylene, the mixture is heated to 130 C. with stirring, and 98 g. /2 mol) of pure tetrapropyl diborane are added dropwise under nitrogen. With continued stirring, the temperature is raised to 140 0., whereby a strong evolution of hydrogen sets in. The temperature is maintained until no further hydrogen escapes. The product is then cooled, filtered and Washed with petroleum ether. The dry crude product is dissolved in cold glacial acetic acid, the filtered solution precipitated by stirring into water, and the precipitate dried. B-dipropyl-boron-oxazolidone obtained in practically quantitative yield is stable to air. The reaction proceeds according to the following equation:

We claim: 1. The process for preparing boron compounds of the formula wherein n is a positive integer from 1 to 2, R is an alkyl radical and R is selected from the group consisting of alicyl, aminoalkyl, alkylaminoalkyl, dialkylaminoalkyl, alkoxyalkyl, aryl, haloaryl, aminoaryl, acyl and acylated radicals selected from the group consisting of aminoalkyl, alkylaminoalkyl, dialkylaminoalkyl, alkoxyalkyl, aryl, haloaryl and aminoaryl, which comprises reacting an alkyl diborane of the formula wherein m is a positive integer from 1 to 4, with a hydroxyl group containing compound of the formula ROH, wherein R and R are as defined above, and recovering the boron compound R,,B(OR') thus formed.

2. Process for preparing dipropyl boric acid butyl ester, which comprises reacting tetrapropyl diborane with n-butanol in an inert atmosphere, and recovering the dipropyl boric acid butyl ester thus formed.

3. Process for preparing dipropyl boric acid propyl ester, which comprises reacting tetrapropyl diborane with n-propanol in an inert atmosphere, and recovering the dipropyl boric acid propyl ester thus formed.

4. Process for preparing dipropyl boric acid phenyl ester, which comprises reacting tetrapropyl diborane with phenol in an inert atmosphere, and recovering the dipropyl boric acid phenyl ester thus formed.

5. Process for preparing dipropyl boric acid-3-methoxybutyl ester, which comprises reacting tetrapropyldiborane with 3-methoXy-butanol-1 in an inert atmosphere, and recovering the dipropyl boric acid-3-methoxybutyl ester thus formed.

6. Process for preparing dipropyl methoxyaceto boric acid, which comprises reacting tetrapropyldiborane with methoxy acetic acid, and recovering the dipropyl methoxyaceto boric acid thus formed.

7. Process for preparing fi-dipropyl-boron-oxazolidone, which comprises reacting tetrapropyldiborane with glycine, and recovering the ,B-dipropyl-boron-oxazolidone thus formed.

8. A B-dialkyl-boro-oxazolidone.

References Cited in the file of this patent UNITED STATES PATENTS 2,961,469 Klein et a1. NOV. 22, 1960 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 133,951 May 19-,1964

Karl Niitzel et a1.

It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 3, lines 51 to 6O the equation should appearas shown below instead of as in the patent:

3 'Z\ 3 B 0 o -ca (C H BH+CH .'0.( I-I.CH .CHOH-- +H2 CH a-cn same column 3; line 72, for "aninoalcohols" read aminoalcohols column 4, line 5 for "of" read or column 5 lines 3 to 10 the equation should appear as shown below instead of as in the patent:

B (C H B H +2CH .OCH(CH 9CH H 0H92 l) osca H 2 CH (SH-CH Signed and sealed this 3rd day of November 1964 (SEAL) Attest:

ERNEST W, SWIDER EDWARD J. BRENNER Att'esting Officer Commissioner of Patents 

1. THE PROCESS FOR PREPARING BORON COMPOUNDS OF THE FORMULA
 8. A B-DIALKYL-BORO-OXAZOLIDONE. 